Surface treating appliances, for example vacuum cleaners can separate dirt and dust from an airflow without the use of a filter bag. These so-called bagless vacuum cleaners are very popular. Most bagless vacuum cleaners use cyclonic or centrifugal separation to spin dirt and dust from the airflow. By avoiding the use of a filter bag as the primary form of separation, it has been found to be possible to maintain a consistently high level of suction, even as the collecting chamber fills with dirt.
The principle of cyclonic separation in domestic vacuum cleaners is described in a number of publications including EP 0 042 723. In general, an airflow in which dirt and dust is entrained enters a first cyclonic separator via a tangential inlet which causes the airflow to follow a spiral or helical path within a collection chamber so that the dirt and dust is separated from the airflow. Relatively clean air passes out of the chamber while the separated dirt and dust is collected therein. In some applications, the airflow is then passed through a second and possibly a third stage of cyclonic separation which is capable of separating finer dirt and dust than the upstream cyclone. The airflow is thereby cleaned to a greater degree so that, by the time the airflow exits the cyclonic separating apparatus, the airflow is almost completely free of dirt and dust particles.
Small cyclones can be desirable as they may be able to separate smaller particles of dust. In particular it has been found that small tip (dirt outlet) diameters on cyclones can increase separation efficiency. However, it has also been found that as the cyclones decrease in size there is an increased risk of them blocking, which would impact of the overall separation efficiency of the surface treating appliance.